The present invention relates to real time monitoring of the condition of a fluid in a vessel as, for example, oil in the sump of an internal combustion engine or a power transmission. An example of such a device is that shown and described in copending application of Robert A. Bauer, et al. xe2x80x9cFLUID CONDITION MONITORxe2x80x9d, Ser. No. 09/220,556, filed Dec. 23, 1998, now U.S. Pat. No. 6,278,281, and assigned to the assignee of the present invention. The aforesaid Bauer, et al. application describes monitoring fluid condition with a probe having spaced parallel electrodes preferably in the form of parallel plates and exciting the probe sequentially at a first low and a second high voltage and measuring the difference of the magnitude in current at the first and second excitations. The difference in measured current is then compared with stored values in a lookup table of values of the difference in current for known fluid conditions; and, the condition of the fluid then determined in real time. A microcomputer then outputs a signal if the measured fluid condition is at a pre-designated threshold, as for example, one not suitable for further use.
The parallel plate probe of the aforesaid Bauer, et al. application, although generally useful, has been found somewhat cumbersome and difficult to install in certain closed fluid vessels such as engine oil sumps and power transmission housings inasmuch as the probe must have sufficient electrode surface area, be robust, reliably sealed to prevent loss of fluid and able to withstand the elevated temperatures of engine and power transmission lubricant. The aforesaid parallel plate type probe has been found prohibitively large in engine and transmission lubricant monitoring applications inasmuch as the required surface area of the electrode plates has dictated the minimum size; and, this has resulted in a requirement prohibitively large opening or aperture for a probe insertion in an engine sump or transmission casing.
Accordingly, it has been desired to provide a probe assembly for fluid monitoring particularly by relatively low voltage probe excitation at fractional Hertz frequencies and which is sufficiently small and rugged for insertion in a minimally sized opening in the fluid vessel and particularly an engine sump or transmission casing.
The present invention provides a probe for relatively low voltage, low current monitoring of fluid condition in which fractional Hertz probe excitation is utilized for measuring probe current.
The probe assembly of the present invention has a configuration which enables the probe to be inserted through an aperture or opening having a minimal size and thus is particularly suitable for installation in an engine oil sump or power transmission casing. The probe of the present invention employs a pair of electrodes in wire form which are spirally wound on a support or core for immersion through the aperture in the vessel and into the fluid to be monitored. The ends of the electrodes are attached to leads which extend through the support structure, preferably in the form of a threaded plug, which is inserted in the fluid vessel opening and sealed therein. In one embodiment, the spiral wires are wound in spaced helical configuration. In a variation, the spiral winding has a region of a first uniform pitch another region is wound at a second uniform pitch of about twice the first pitch spacing. In another embodiment, the pair of wire electrodes are wound together in uniformly spaced parallel arrangement at a desired uniform pitch.
The probe assembly of the present invention thus lends itself to insertion in the wall of the fluid vessel through a minimally sized opening; and, fabrication and installation of the probe are greatly simplified.